In mouse myelin there are 4 myelin basic proteins (MBPs) with molecular weights of 21.5K, 18.5K. 17K, and 14K. Bovine myelin contains the 21.5K and 18.5K MBPs. The 18.5K bovine MBP (for which the sequence is known) contains the sequence of the 21.5K MBP except for a domain of 25-35 residues which is deleted. We will determine the exact location and amino acid sequence of this domain by sequencing tryptic and CNBr fragments of the 21.5K and 18.5K proteins. We will determine the extent and nature of MBP polymorphism in other species by using radioimmunoassay to identify different MBPs and by using specific chemical and enzymatic cleavage reactions and two dimensional tryptic fingerprinting to determine their structural interrelationships. We will develop a system for in vitro translation of MBP mRNA from mouse brain and we will characterize the primary translation products to determine whether post-translational processing is involved in MBP biosynthesis. The relative proportions of the 4 mouse MBPs change during myelination, from predominantly 21.5K MBP initially to predominantly 14K MBP in the latter stages. In order to determine whether this is due to changes in the proportions of specific MBP mRNAs, we will use the translation system to measure the amount of MBP mRNA present in the mouse brain at different times during myelination and to determine which proteins it encodes at each age. In order to determine whether MBP polymorphism has any functional signficance in relation to myelin morphogenesis, we will compare the interactions of the different MBPs with various lipids - using equilibrium dialysis in organic solvents to compare their lipid binding capcities and using lactoperoxidase catalyzed iodination and controlled proteolysis to study their conformations in liposomes. Assembly of MBP into myelin apears to involve intracellular pre-myelin vesicles (PMVs). We will isolate PMVs from normal mouse brain and from jimpy mutant mouse brain (in which they accumulate) and characterize them in order to determine their role in myelin biogenesis. We will develop a system to study the process of membrane fusion between PMVs and myelin.